Hysteretic reduction in ASIC boost converter with fixed level
By combining inductive elements, semiconductor switching elements, and current sensors, and utilizing hysteresis control technology, the problem of discontinuous current in the driver within the dimming range is solved, ensuring stable operation of the electronic transformer and LED lights and preventing light output flicker.
Patent Information
- Application Number
- CN202480055953.X
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Priority Date
- 2023-09-04
- Filing Date
- 2024-08-23
- Publication Date
- 2026-03-27
AI Technical Summary
Existing drivers cannot maintain continuous current within the dimming range, causing electronic transformers to malfunction or even be damaged, affecting the normal power supply and light output of LED lights.
By employing a combination of inductors, semiconductor switches, unidirectional switches, and current sensors, and using hysteresis control technology, the current is sensed and the opening and closing of the semiconductor switches are controlled to ensure that the current remains continuous throughout the entire dimming range.
It achieves continuous current within the dimming range, improves the stability of the electronic transformer and the normal power supply of LED lights, and avoids flickering in light output.
Smart Images
Figure CN121753478A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to a driver. This invention also relates to a lighting system. Background Technology
[0002] Electronic transformers are commonly used to convert mains voltage to a lower voltage level to power low-voltage halogen lamps. For example, a 12V MR16 lamp is powered by an electronic transformer. Halogen lamps are replaced by LED lamps. LED lamps require significantly less power than halogen lamps. Electronic transformers, especially self-oscillating electronic transformers, require a minimum output current to operate properly. If the output current is too low, the electronic transformer will not function properly and may even be damaged. Because LED lamps require a small amount of power, they can draw current below the minimum current required by the electronic transformer. Therefore, the electronic transformer may not function properly, and the LED lamp will not be powered correctly, potentially causing flickering light output. It is highly desirable to provide a driver that draws current from the electronic transformer that remains above the minimum current required by the electronic transformer. Summary of the Invention
[0003] The object of this invention is to provide a driver that can draw continuous current from an electronic transformer throughout its dimming range.
[0004] To overcome this problem, in a first aspect of the invention, a driver for driving a lighting load is provided. The driver includes:
[0005] Inductive components;
[0006] Semiconductor switching elements;
[0007] One-way switching element,
[0008] It can be coupled to the output of a lighting load;
[0009] Controller, which controls semiconductor switching elements; and
[0010] A current sensor is arranged to sense the current at the output and the semiconductor switching element;
[0011] The inductor, semiconductor switch, and unidirectional switch are coupled to each other. The semiconductor switch is arranged to charge the inductor when it is closed, and the unidirectional switch is arranged to discharge the inductor to the output when it is open.
[0012] The current sensor includes a first sensing element and a second sensing element, wherein the first and second sensing elements are coupled in series with a semiconductor switching element, and the lighting load can be coupled between the output terminal and the node between the first and second sensing elements.
[0013] The series combination of the first sensing element and the second sensing element is used to sense the current in the inductor when the semiconductor switching element is closed, and the second sensing element is used to sense the current in the inductor when the semiconductor switching element is open.
[0014] The controller is arranged as follows:
[0015] When the semiconductor switching element is closed, and the current in the inductor element exceeds a first threshold, the semiconductor switching element is opened, and
[0016] When the semiconductor switching element is turned off, the semiconductor switching element is turned off when the current through the inductor element drops below a second threshold, wherein the second threshold is lower than the first threshold.
[0017] A driver is provided to power a lighting load via an output terminal. The driver has an inductor, a semiconductor switching element, and a unidirectional switching element. They can be configured as a switch-mode power supply. These components are arranged such that when the semiconductor switching element is closed, the inductor is charged. This means that the current through the inductor increases. Furthermore, when the semiconductor switching element is open, the energy stored in the inductor is released to the output terminal, and the current through the inductor decreases. A controller is provided to control the semiconductor switching element. The controller can turn the semiconductor switching element on and off. Preferably, the controller is used to control the semiconductor switching element using hysteresis control. This is done by using a sense signal and comparing it with an upper threshold and a lower threshold. In this example, a current sensor is provided. The current sensor has a series combination of a first sensing element and a second sensing element to sense the current through the inductor when the semiconductor switching element is closed. The second sensing element is used to sense the current in the inductor when the semiconductor switching element is open. Therefore, the state of the semiconductor switching element determines which sensing elements are used to sense the current through the inductor. When the current through the inductor exceeds the first threshold, the controller is arranged to open the semiconductor switching element if the semiconductor switching element is closed. The first threshold determines the peak current through the inductor. As the semiconductor switching element is turned off, the current begins to decrease because the unidirectional switching element supplies current to the output through the inductor, and thus ultimately to the lighting load. The current through the inductor continues to decrease until it falls below the second threshold. At this point, the controller closes the semiconductor switching element. This control method is called hysteresis control, using a first to second threshold and a second bottom threshold. Sensing the current using both the first and second sensing elements when the semiconductor switching element is closed provides an accurate determination of the current reaching the first threshold. By coupling the lighting load between the output and node of the first and second sensing elements, the current sensed when the semiconductor switching element is turned off is accomplished solely by the second sensing element. Using the second sensing element to sense the current provides a lower sensing voltage with a similar current amplitude. Therefore, the lower threshold is reached faster than when sensed using both the first and second sensing elements. This allows for achieving a smaller hysteresis without having to change any hysteresis parameters in the controller. This means that the current ripple in the inductor can be further reduced without any modification to the controller.
[0018] In another example, an inductor, a semiconductor switch, and a unidirectional switch form a boost converter.
[0019] Preferably, the inductor, semiconductor switch, and unidirectional switch form a switch-mode power converter. More preferably, the switch-mode power converter is a boost converter.
[0020] In another example, the unidirectional switching element is a diode.
[0021] In its simplest form, a unidirectional switching element is a diode. A unidirectional switching element can also be a MOSFET that operates synchronously. This means that a MOSFET will behave similarly to a diode.
[0022] In another example, the first sensing element includes a first resistor, and the second sensing element includes a second resistor.
[0023] In a very simple form, the current sensor has a first sensing element and a second sensing element, the first sensing element having a first resistor for sensing current, and the second sensing element having a second resistor for sensing current. Preferably, the resistor is a resistor.
[0024] In another example, the ratio between the first threshold and the second threshold is less than the ratio between the first resistor and the second resistor.
[0025] Preferably, the ratio between the first threshold and the second threshold is less than the ratio between the first resistor and the second resistor. If this is no longer true, the controller's hysteresis will no longer function, and therefore the driver will malfunction.
[0026] In yet another example, the first sensing element includes:
[0027] The first resistor and the second resistor are connected in series;
[0028] The first switch is adapted to shunt current to the first resistor, and
[0029] The second switch is adapted to shunt current to the second resistor.
[0030] The controller is configured to control the first and second switches based on the current required by the lighting load.
[0031] The driver can be adapted to provide different output currents to lighting loads at different light output terminals. This means the driver provides adjustable current to the lighting load. The hysteresis band will vary at each dimming or current level. The number of resistors forming the first sensing element can be switched according to the dimming level.
[0032] In another example, the controller is configured to close either the first or the second switch when the current required by the lighting load exceeds a current threshold.
[0033] At higher output power, the total resistance of the first sensing element is kept as low as possible. Preferably, the first sensing element is provided with the lowest possible resistance at the maximum power supplied to the output.
[0034] In another example, the controller is configured to disconnect the first and second switches when the current required by the lighting load drops below a current threshold.
[0035] The lower the output power, the greater the resistance supplied to the first sensing element. Preferably, all resistances are utilized at the lowest possible power supplied to the output.
[0036] In another example, the controller is arranged to open and close the first and second switches, such that the current through the inductive element remains continuous, regardless of the amount of current required by the lighting load.
[0037] Preferably, the controller controls the first switch and the second switch such that the current through the inductor remains continuous throughout the dimming range, i.e., it does not drop to zero.
[0038] In another example, the first sensing element includes a variable resistor.
[0039] To provide a uniform reduction in hysteresis across the dimming range, a variable resistor can be used to continuously change the resistance within the dimming range. For example, the resistance can be increased as the peak current decreases. An example of a variable resistor could be a transistor operating in its linear region.
[0040] In another example, the driver also includes a buck converter coupled between the output and the output of a unidirectional switching element, wherein the unidirectional switching element is arranged to discharge the inductive element to the lighting load via the buck converter.
[0041] An additional buck converter can be placed between the output of the buck converter and the output of the unidirectional switching element. As an example, a boost converter can be used as the first stage, and the buck converter can be coupled to the output of the buck converter. The boost converter can be used to draw continuous current from the electronic transformer. The boost converter can generate a bus voltage at its output (e.g., the output of the unidirectional switching element), which is then provided to the buck converter. The buck converter is used to generate a regulated current to the lighting load. The driver allows for good current control at the input and good current regulation at the output.
[0042] In another example, a lighting system is provided. The lighting system includes a driver and a lighting load.
[0043] Preferably, a lighting system is provided. When connected to an electronic transformer, the driver has optimized performance together with the lighting load.
[0044] In another example, the lighting load includes LEDs.
[0045] Preferably, the lighting load has an LED. The LED provides light in an energy-efficient manner, and the light output can be controlled by providing a regulated current to the LED.
[0046] In another example, the lighting system may be connected to an electronic transformer, wherein the controller is arranged to continuously maintain the current drawn from the electronic transformer above a threshold.
[0047] For stable operation, electronic transformers require a minimum amount of current. Therefore, it is desirable for the driver to draw sufficient current. By reducing hysteresis according to the present invention, the current drawn by the driver can be controlled to remain continuous over a wider dimming range, thus improving compatibility with electronic transformers.
[0048] In another example, a threshold is defined above the current level, allowing the electronic transformer to operate continuously in steady mode.
[0049] Preferably, a threshold is defined for the driver to regulate the current to keep it above the threshold, thereby ensuring stable operation of the electronic transformer. Attached Figure Description
[0050] Examples of the invention will now be described with reference to the accompanying drawings, in which:
[0051] Figure 1 An example of a commonly used boost converter is shown.
[0052] Figure 2 Another example of a commonly used boost converter is shown.
[0053] Figure 3 An example graph showing the inductor current and sensor voltage in a common boost converter is shown.
[0054] Figure 4 An example of a driver is shown.
[0055] Figure 5 An example is shown illustrating the curves of inductor current and sensor voltage in a boost converter.
[0056] Figure 6 The graph shows the decrease in hysteresis over the peak current range.
[0057] Figure 7 The detailed configuration of the first sensing element is shown.
[0058] Figure 8 The graph shows the decrease in hysteresis over the peak current range. Detailed Implementation
[0059] The invention will be described with reference to the accompanying drawings.
[0060] It should be understood that the detailed description and specific examples, while indicating exemplary embodiments of the apparatuses, systems, and methods, are for illustrative purposes only and are not intended to limit the scope of the invention. These and other features, aspects, and advantages of the apparatuses, systems, and methods of the present invention will become more readily apparent from the following description, the appended claims, and the accompanying drawings. It should also be understood that the drawings are merely schematic and not drawn to scale. Furthermore, it should be understood that the same reference numerals are used throughout the drawings to denote the same or similar parts.
[0061] Figure 1 The circuit diagram of a commonly used boost converter is shown. The boost converter has an inductor L1, a MOSFET M1, and a diode D1. A capacitor C1 is placed in parallel with the lighting load LED to filter out the high-frequency current ripple of the LED. A current sensor R1 is used to sense the current flowing through the inductor L1 and the MOSFET M1. A controller 1 uses the sensed current to control the MOSFET. In this example, the controller can keep the MOSFET M1 closed until the current sensor senses a current exceeding a threshold. This control is also called threshold control. The time that the MOSFET M1 remains off is fixed. Therefore, the controller provides an on-time based on a threshold level, with more power in the load causing an increased threshold and vice versa, and provides a fixed off-time. The disadvantage of this control is that the fixed off-time may cause the current through the inductor L1 to drop to zero at any moment. This is also known as discontinuous current control mode. When such a boost converter is connected to an electronic transformer, the current discontinuity causes the electronic transformer to stop working and causes the electronic transformer to continuously attempt to restart. Especially for self-oscillating electronic transformers, the current to the driver is also used to maintain the proper operation of the semiconductor switching elements in the electronic transformer.
[0062] Figure 2 It shows the provision of control Figure 1 Examples of improved boost converters with different driver methods. Boost converters have... Figure 1The boost converter is similarly coupled with inductor L1, diode D1, and MOSFET M1. Sensing resistor R1 is placed in a different position. In this position, the inductor current can be continuously measured. When MOSFET M1 is closed, the current through inductor L1 flows through MOSFET M1 and resistor R1. When MOSFET M1 is open, the current through inductor L1 flows through diode D1, the load LED, capacitor C1, and sensing resistor R1. Therefore, placing sensing resistor R1 in this position allows for the measurement of the maximum and minimum inductor current, thus enabling hysteresis current control. For hysteresis current control, two thresholds are determined: a maximum current threshold and a minimum current threshold. Controller 1 uses the maximum current threshold to open MOSFET M1 and the minimum current threshold to close MOSFET M1. Controller 1 is typically a dedicated IC used to control the driver, such as a boost converter. This specific IC can also be referred to as an application-specific integrated circuit (ASIC). Such ICs typically have a built-in fixed minimum hysteresis timing. For example, the IC provides regulation of the peak inductor current and a hysteresis of 40mV, which will be supplied to the voltage provided by the current sensor R1. This means that the second threshold is set 40mV lower than the first threshold. For example, the sensing resistor R1 has a resistance of 100mΩ. The maximum peak current can be set to 1.45A, resulting in a sensing voltage of 145mV. The first threshold is therefore set to 145mV. The second threshold is then set to 145mV - 40mV = 105mV. The current corresponding to the second threshold is 105mV / 100mΩ. =1.05A. Therefore, the inductor current hysteresis is 0.4A. This hysteresis is the same throughout the driver's dimming range. The output power is reduced by lowering the first threshold level. Therefore, this also lowers the second threshold level. Reducing the output power will eventually cause the inductor current to drop below the current value that allows the electronic transformer to operate stably.
[0063] Figure 3 An exemplary waveform is shown illustrating the sensed current V(s) and the actual current I(L1) through inductor L1. A first threshold is set at a voltage of approximately 145mV, and a second threshold is set at 105mV. This is reflected by controlling MOSFET M1 such that the peak current through inductor L1 corresponding to the first threshold is approximately 1.45A and the bottom current corresponding to the second threshold is 1.05A.
[0064] The inventors understand that reducing hysteresis will increase the second threshold, allowing for deeper dimming with similar drivers. Hysteresis cannot be adjusted by the controller itself because it is a fixed level. Therefore, circuit modifications are required. The inventors have discovered that providing different ways of sensing the current through the inductor allows for hysteresis adjustment without changing the control and feedback circuitry.
[0065] Figure 4 A circuit diagram of a driver with an improved current sensor is shown. The driver has an inductor element L1 shown as an inductor, a unidirectional switching element D1 shown as a diode, and a semiconductor switching element M1 shown as a MOSFET. In this example, these components form a boost converter. The output of the boost converter is buffered by a capacitor C1. Current sensors R2 and R3 are provided to sense the current through the inductor element L1. The current sensor is divided into two sensing elements. The first sensing element R2 has a first sensing resistor. The second sensing element R3 has a second sensing resistor. When the controller 1 closes the semiconductor switching element M1, the current through the inductor element L1 flows through the semiconductor switching element M1. In this example, the current flows through resistors R2 and R3. Therefore, the current sensor uses both the first sensing element R2 and the second sensing element R3. When the controller 1 opens the semiconductor switching element M1, the current through the inductor element L1 flows through the unidirectional switching element D1, and thus through the load LED and the capacitor C1. The current sensor uses only the second sensing element R3 because no current flows through the first sensing element R2. When semiconductor switch M1 is open and when semiconductor switch M1 is closed, the current sensor provides a voltage to controller 1 with a voltage step that reaches a lower voltage level by sensing the current with different sensing elements. For example, for the same current amplitude, the voltage provided by the current sensor when semiconductor switch M1 is closed will be greater than the voltage provided by the current sensor when semiconductor switch M1 is open. Therefore, closing or opening semiconductor switch M1 will result in a stepped change in the voltage generated by the current sensor. This stepped change will provide a reduction in hysteresis because the stepped change will allow the second threshold to be reached more quickly. The larger the voltage step, the earlier the second threshold is reached, and therefore the lower the hysteresis. Figure 5 An example is provided of how this stepwise change can reduce lag.
[0066] Figure 5An example graph illustrating the inductor current and sensor voltage in a boost converter is shown. The inductor current is the current flowing through inductor L1. The sensor voltage is the voltage generated by the current sensor. When semiconductor switch M1 is closed, the current through inductor L1 increases. Controller 1 can be configured to compare the voltage provided by the current sensor with a reference voltage. In this example, the reference voltage can be set to 145mV. In this example, the reference voltage can be equal to a first threshold. The current is sensed by a first sensing element R2 and a second sensing element R3. Resistor R2 has a resistance of 25mΩ, and resistor R3 has a resistance of 75mΩ. When the current reaches an amplitude of 1.45A, controller 1 receives a voltage of 145mV from current sensors R2 and R3. The 145mV voltage corresponds to the first threshold; therefore, controller 1 will turn off semiconductor switch M1. Figure 5 In the diagram, the disconnection of semiconductor switch M1 can be observed where the current through inductor L1 reaches its peak. After semiconductor switch M1 is disconnected, the current through inductor L1 begins to decrease. Since the decreasing current flows through unidirectional switch D1, current sensors R2 and R3 use only the second sensing element R3 to sense the current through the inductor. The total sensing resistance of the current sensors decreases from 100mΩ to 75mΩ. Therefore, directly after semiconductor switch M1 is disconnected, the voltage supplied by current sensors R2 and R3 drops from approximately 36mV to approximately 109mV. This is not a precise transition because the inductor begins to commutate during the disconnection of semiconductor switch M1, which takes some time. After this voltage step to approximately 109mV, the current through inductor L1 continues to decrease until current sensors R2 and R3 supply a voltage corresponding to the second threshold level to controller 1. This determines that the second threshold is 40mV lower than the first threshold. This results in a second threshold voltage of 105mV. This corresponds to a current of 1.4A through inductor L1. Without any modifications, the current through inductor L1 would be 1.05A, as... Figure 3 As shown. Therefore, the hysteresis is reduced by 0.35A. The current through inductor L1 remains high. Therefore, the current supplied by the electronic ballast will remain high, resulting in improved compatibility.
[0067] Figure 6The reduction in hysteresis over the peak current range is illustrated in a theoretical example. For example, the first threshold is set to 145mV, and the second threshold is set to 105mV. Therefore, the hysteresis is set to 40mV. The first sensing element R2 has a resistance of 25mΩ, and the second sensing element R3 has a resistance of 75mΩ. In this example, the peak current is changed, and its effect on the hysteresis is predicted. Changing the peak current amplitude results in a sudden change in the voltage drop after the semiconductor switching element M1 is turned off. A larger voltage drop results in a larger reduction in hysteresis. Therefore, a higher peak current will result in a higher voltage drop, and thus a larger reduction in hysteresis. This can be achieved by... Figure 6 It is clear that a decrease in peak current leads to a relative decrease in hysteresis. For example, a peak current of 1.5A results in a 93.75% reduction in hysteresis, while a peak current of 0.75A results in a 46.9% reduction. It can be seen that in this configuration, at a peak current of 1.6A, the hysteresis is reduced by 100%. This is considered the physical boundary of hysteresis reduction. At 100% hysteresis, the semiconductor switching element M1 would switch at an infinitely high speed. Therefore, it is undesirable to achieve 100% hysteresis reduction. Currents above 1.6A disrupt the hysteresis, and the driver will no longer function. Therefore, it is desirable that the ratio between the first and second thresholds be less than the ratio between the resistances of the first and second sensing elements.
[0068] Figure 7 An example of a detailed configuration of the first sensing element R2 is shown. In this example, the sensing element is provided with multiple resistors coupled in series. Resistors R2_a, R2_b, and R2_c form the resistance of the first sensing element R2. In this example, each resistor is provided with a shunt switch. Switch SW1 is connected in parallel with resistor R2_a, switch SW2 is connected in parallel with resistor R2_b, and switch SW3 is connected in parallel with resistor R2_c. Since at least one resistor needs to be placed between the semiconductor switching element M1 and the second sensing element R3 at any given time, one of switches SW1, SW2, or SW3 can be omitted. Figure 6 As can be seen, the reduction in hysteresis decreases as the peak current decreases. The main reason for reducing the peak current is to supply lower power to the lighting load. By reducing the peak current, the total current is also reduced. This brings the current closer to the minimum operating current of the electronic transformer. An increase in hysteresis could cause the current to drop below this minimum operating current, leading to electronic transformer failure. Therefore, it is further desirable to optimize hysteresis reduction at lower current levels.
[0069] As described above, when the semiconductor switching element M1 is off, the peak current determines the amount of voltage drop. Therefore, a decrease in the peak current will lead to a decrease in the voltage drop, and thus a decrease in the hysteresis reduction. By increasing the resistance of the first sensing element R2, the voltage drop increases again. As an example and for simplicity, resistors R2_a, R2_b, and R2_c are identical and have a resistance of 25mΩ. Preferably, only one resistor is effective at high peak currents. This can be achieved by closing both switches and keeping one switch open. In this case, the hysteresis reduction will be related to... Figure 6 The hysteresis reduction is the same as shown. If the hysteresis reduction is no longer sufficient, for example, the peak current has decreased to a first peak current threshold, one of the closed switches will open. Therefore, the resistance of the first sensing element R2 will increase to 50mΩ, resulting in an increase in voltage drop and an increase in hysteresis reduction. Similarly, further reducing the peak current until a second peak current threshold is reached will cause all switches to open. The resistance of the first sensing element R2 will increase to 75mΩ, again resulting in an increase in voltage drop and an increase in hysteresis reduction.
[0070] Figure 8 A graph showing the decrease in hysteresis within the dimming range is shown. The reduction in peak current determines the dimming level. In this example, the value of the hysteresis reduction is based on when using... Figure 7 The values described in the circuit are derivable. At a peak current of 1.5A, the hysteresis is reduced by approximately 94%. Reducing the peak current results in a further reduction in hysteresis. At a peak current of 0.75A, one of the switches is open, and the first sensing element R2 has a total resistance of 50mΩ. Therefore, when an additional switch is open, the hysteresis reduction at a peak current of 0.75A changes from 47% to 94%. The peak current can be further reduced. At a peak current of 0.25A, the hysteresis is reduced to 31%. At this peak current amplitude, all switches are open. This results in a total resistance of 75mΩ for the first sensing element R2. The hysteresis reduction changes from 31% to 47%.
[0071] As an additional improvement, the driver can be equipped with a buck converter for driving the lighting load LEDs. For example, the output of a boost converter can be coupled to the input of a buck converter. Thus, the boost converter can be optimized to draw well-regulated current from the electronic transformer, and the buck converter can then be configured to provide a reasonably regulated current to the lighting load.
[0072] Preferably, the driver is integrated into the lighting system, which also includes the lighting load LED. Preferably, the lighting load is a low-power load such as an LED or a laser diode.
[0073] By studying the accompanying drawings, the disclosure, and the appended claims, those skilled in the art can understand and implement other variations of the disclosed embodiments in practicing the claimed invention. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite articles "a" or "an" do not exclude a plurality. The fact that certain measures are recited in mutually different dependent claims does not imply that combinations of these measures cannot be advantageously used. Any reference numerals in the claims should not be construed as limiting the scope.
Claims
1. A driver for driving a lighting load (LED), the driver comprising: Inductor (L1); Semiconductor switching element (M1); One-way switching element (D1); The output end can be coupled to the lighting load (LED). Controller (1), for controlling the semiconductor switching element (M1), and A current sensor is arranged to sense the current at the output terminal and the semiconductor switching element (M1). The inductor (L1), the semiconductor switch (M1), and the unidirectional switch (D1) are coupled to each other, and the semiconductor switch (M1) is arranged to charge the inductor (L1) when the semiconductor switch (M1) is closed, and the unidirectional switch (D1) is arranged to discharge the inductor (L1) to the output terminal when the semiconductor switch (M1) is open. The current sensor includes a first sensing element (R2) and a second sensing element (R3), wherein the first sensing element (R2) and the second sensing element (R3) are coupled in series with the semiconductor switching element (M1), and the lighting load (LED) can be coupled between the output terminal and the node between the first sensing element (R2) and the second sensing element (R3). The series combination of the first sensing element (R2) and the second sensing element (R3) is used to sense the current in the inductor (L1) when the semiconductor switch element (M1) is closed, and the second sensing element (R3) is used to sense the current in the inductor (L1) when the semiconductor switch element (M1) is open. The controller (1) is arranged as follows: When the semiconductor switching element (M1) is closed, and when the current in the inductor element (L1) exceeds a first threshold, the semiconductor switching element (M1) is opened, and When the semiconductor switching element (M1) is turned off, the semiconductor switching element (M1) is turned off when the current through the inductor element (L1) drops below a second threshold, wherein the second threshold is lower than the first threshold.
2. The driver according to claim 1, wherein the inductor (L1), the semiconductor switch (M1), and the unidirectional switch (D1) form a boost converter.
3. The driver according to any one of the preceding claims, wherein the unidirectional switching element (D1) is a diode.
4. The driver according to any one of the preceding claims, wherein the first sensing element (R2) includes a first resistor, and the second sensing element (R3) includes a second resistor.
5. The driver according to claim 4, wherein the ratio between the first threshold and the second threshold is less than the ratio between the first resistor (R2) and the second resistor (R3).
6. The driver according to any one of the preceding claims, wherein the first sensing element (R2) comprises: A series combination of the first resistor (R2_a) and the second resistor (R2_b); The first switch (SW1) is adapted to shunt current to the first resistor, and The second switch (SW2) is adapted to shunt current to the second resistor. The controller (1) is configured to control the first switch (SW1) and the second switch (SW2) based on the amount of current required by the lighting load (LED).
7. The driver according to claim 6, wherein the controller (1) is arranged to close the first switch (SW1) or the second switch (SW2) when the current required by the lighting load (LED) exceeds a current threshold.
8. The driver according to claim 7, wherein the controller (1) is arranged to disconnect the first switch (SW1) and the second switch (SW2) when the current required by the lighting load (LED) drops below the current threshold.
9. The driver of claim 7, wherein the controller is arranged to open and close the first switch (SW1) and the second switch (SW2) such that the current through the inductor (L1) remains continuous, regardless of the amount of current required by the lighting load (L1).
10. The driver of claim 1, wherein the first sensing element (R2) comprises a variable resistor.
11. The driver according to any one of the preceding claims further includes a buck converter coupled between the output terminal and the output terminal of the unidirectional switching element (D1), wherein the unidirectional switching element (D1) is arranged to discharge the inductor element (L1) to the lighting load (LED) via the buck converter.
12. A lighting system comprising a driver according to any one of the preceding claims and the lighting load.
13. The lighting system of claim 12, wherein the lighting load comprises an LED.
14. The lighting system of claim 13, wherein the lighting system is connectable to an electronic transformer, wherein the controller (1) is arranged to continuously maintain the current drawn from the electronic transformer above a threshold.
15. The lighting system of claim 14, wherein the threshold is defined as being above the current level, causing the electronic transformer to operate continuously in a stable mode.